Katie Couric, whose husband died of colon cancer, famously underwent a colonoscopy on air to highlight the importance of early detection. So when she addressed the packed Library of American Broadcasting’s annual event at the Grand Hyatt the other night, the crowd howled when she said, “It is often said that the greatest responsibility of a broadcaster is to shine a light in dark places — which brings me to my favorite subject!” Hon ored posthumously were Ed McMahon, radio legend Paul Harvey and Walter Cronkite. Besides Couric, documentary maker Ken Burns was saluted while Charles Osgood emceed.